丁香园AV

Synopsis

A major theme in the past couple of decades of research in condensed matter physics-archive has been to understand properties of quantum materials using the language of geometric (or 鈥淏erry鈥�) phases and connections. Nonlinear optical properties, such as second harmonic generation, are examples of phenomena that depend crucially on the band structure geometry. In this talk, I will report on the recent discovery of the highest-known second harmonic susceptibility in the topological metal compound TaAs. I will further present a new theorem which relates a sum rule for the second order nonlinear conductivity with the third cumulant (or 鈥渟kewness鈥�) of the electronic wavefunction. This theorem suggests the existence of ultimate upper bounds allowed on the nonlinear optical conductivity of crystalline materials.